The present invention relates in general to detecting the presence of rainfall on a vehicle window for automatic activation of a wiper system, and, more specifically, to rain detection by mechanical sensing and digital processing of acoustic metrics of a sensed vibration signal.
Automatic windshield wiper control systems that adjust wiper operation/speed according to the presence of moisture or the intensity of rainfall on the windshield are known in the art. Such systems typically include an electronic control module that is connected to a wiper arm drive motor. The control module adjusts the operation and speed of the wiper arm drive motor in response to sensory input. Optical sensors are the most common choice for sensing moisture. Placement on a window (e.g., near the rear view mirror) allows a sensor to detect moisture based on changes of light reflection when water is present. However, moisture must be concentrated precisely within the small field of the optical sensor for it to work properly. Dirt or other substances on the windshield can sometimes be interpreted as moisture, falsely triggering the wipers. Moreover, the sensors are relatively expensive and are only useful in connection with rain detection. It would be desirable to improve rain detection performance, reduce sensor costs, shrink packaging size, and adopt a sensor technology that supports other types of functionality.